Prosecutors say the alleged sexual assault of a boy observed by a former Penn State graduate assistant, a key witness in the child sex abuse case against Jerry Sandusky, took place about a year earlier than what was originally alleged, causing defense lawyers for two former Penn State officials to argue that one of the charges should now be dropped.

In a court filing Monday, the attorney general's office determined that the incident in question occurred around February 9, 2001, rather than in March 2002, which was originally listed in the grand jury report.

Tim Curley, Penn State's former athletic director, and Gary Schultz, a former university vice president who oversaw campus police, have been charged with perjury and failing to report the incident.

Attorneys for Curley and Schultz said in a statement that "the Commonwealth charged this case before it knew the facts."

"Now, it is clear that Mike McQueary was wrong in so adamantly insisting that the incident happened the Friday before Spring Break in 2002," the statement said. "Whether or not Mr. McQueary's insistence was the result of faulty memory, or questionable credibility, there is no dispute that the statute of limitations has expired on Count Two, and it will be dismissed."

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Mike McQueary, then a graduate assistant, testified that he told university officials that he saw former coach Sandusky possibly sodomizing a boy, saying that what he saw was "extremely sexual in nature."

Sandusky faces more than 50 counts involving alleged sexual acts with 10 children since 1994.

McQueary, a former Penn State quarterback, testified that he met with Curley and Schultz to inform them about the alleged incident about nine days after first alerting then-head coach Joe Paterno.

Curley, 57, is now on leave, and Schultz, 62, retired in the wake of the allegations. Days after the grand jury presentment came to light, Penn State trustees ousted President Graham Spanier and Paterno amid criticism that they could and should have done more.